Liquid crystal apparatus

ABSTRACT

A liquid crystal apparatus comprises a) a liquid crystal device comprising an electrode matrix composed of scanning electrodes and data electrodes, and a ferroelectric liquid crystal; and b) a driving means. The driving means includes a first drive means for applying a scanning selection signal two or more scanning electrodes apart in one vertical scanning so at to effect in one picture scanning in plural times of vertical scanning, and a second drive means for applying data signals in synchronism with the scanning selection signal. &lt;IMAGE&gt;

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a liquid crystal apparatus, such as adisplay panel or a shutter-array printer, using a ferroelectric liquidcrystal.

Hitherto, there has been well-known a type of liquid crystal displaydevices which comprises a group of scanning electrodes and a group ofsignal or data electrodes arranged in a matrix, and a liquid crystalcompound is filled between the electrode groups to form a large numberof pixels thereby to display images or information.

These display devices are driven by a multiplexing driving methodwherein an address signal is selectively applied sequentially andperiodically to the group of scanning electrodes, and prescribed datasignals are parallely and selectively applied to the group of dataelectrodes in synchronism with the address signals.

In most of the practical devices of the type described above, TN(twisted nematic)-type liquid crystals have been used as described in"Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal"by M. Schadt and W. Helfrich, Applied Physics Letters, Vol. 18, No. 4,pp. 127-128.

In recent years, the use of a liquid crystal device showing bistabilityhas been proposed by Clark and Lagerwall as an improvement to theconventional liquid crystal devices in U.S. Pat. No. 4,367,924; JP-A(Kokai) 56-107216; etc. As the bistable liquid crystal, a ferroelectricliquid crystal (hereinafter sometimes abbreviated as "FLC") showingchiral smectic C phase (SmC*) or H phase (SmH*) is generally used. Theferroelectric liquid crystal assume either a first optically stablestate or a second optically stable state in response to an electricfield applied thereto and retains the resultant state in the absence ofan electric field, thus showing a bistability. Further, theferroelectric liquid crystal quickly responds to a change in electricfield, and thus the ferroelectric liquid crystal device is expected tobe widely used in the field of a high-speed and memory-type displayapparatus, etc.

However, the above-mentioned ferroelectric liquid crystal device hasinvolved a problem of flickering at the time of multiplex driving. Forexample, European Laid-Open Patent Application (EP-A) 149899 discloses amultiplex driving method comprising applying a scanning selection signalof an AC voltage the polarity of which is reversed (or the signal phaseof which is reversed) for each frame to selectively write a "white"state (in combination with cross nicol polarizers arranged to provide a"bright" state at this time) in a frame and then selectively write a"black" state (in combination with the cross nicol polarizers arrangedto provide a "dark" state at this time). In addition to the abovedriving method, those driving methods as disclosed by U.S. Pat. Nos.4,548,476 and 4,655,561 have been known.

In such a driving method, at the time of selective writing of "black"after a selective writing of "white", a pixel selectively written in"white" in the previous frame is placed in a half-selection state,whereby the pixel is supplied with a voltage which is smaller than thewriting voltage but is still effective. As a result, at the time ofselective writing of "black" in the multiplex driving method, selectedpixels for writing "white" constituting the background of a black imageare wholly supplied with a half-selection voltage in a 1/2 frame cycle(1/2 of a reciprocal of one frame or picture scanning period) so thatthe optical characteristic of the white selection pixels varies in each1/2 frame period. As a number of white selection pixels is much largerthan the number of black selection pixels in a display of a black image,e.g., character, on a white background, the white background causesflickering. Occurrence of a similar flickering is observable also on adisplay of white characters on the black background opposite to theabove case. In case where an ordinary frame frequency is 30 Hz, theabove half-selection voltage is applied at a frequency of 15 Hz which isa 1/2 frame frequency, so that it is sensed by an observer as aflickering to remarkably degrade the display quality.

Particularly, in driving of a ferroelectric liquid crystal at a lowtemperature, it is necessary to use a longer driving pulse (scanningselection period) than that used at a 1/2 frame frequency of 15 Hz for ahigher temperature to necessitate scanning drive at a lower 1/2 framefrequency of, e.g., 5-10 Hz. This leads to occurrence of a noticeableflickering due to a low frame frequency drive at a low temperature.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a ferroelectric liquidcrystal apparatus wherein occurrence of flickering caused by a low framefrequency scanning drive, e.g., 15 Hz or below, is suppressed.

Another object of the present invention is to provide a ferroelectricliquid crystal apparatus for realizing a gradational display free fromflickering.

A further object of the present invention is to provide a ferroelectricliquid crystal apparatus with an improved display quality and a broaddriving margin.

According to a first aspect of the present invention, there is provideda liquid crystal apparatus, comprising:

a) a liquid crystal device comprising an electrode matrix composed ofscanning electrodes and data electrodes, and a ferroelectric liquidcrystal; and

b) a driving means including a first drive means for applying a scanningselection signal two or more scanning electrodes apart in one verticalscanning so as to effect one picture scanning in plural times ofvertical scanning, and a second drive means for applying data signals insynchronism with the scanning selection signal.

Herein, a screen for a picture display is defined by the electrodematrix. The term "picture scanning" refers to scanning of all thescanning electrodes constituting or covering all or a prescribed part ofthe screen for providing a desired picture.

According to a second aspect of the present invention, there is provideda liquid crystal apparatus comprising:

a) a liquid crystal device comprising an electrode matrix composed ofscanning electrodes and data electrodes, and a ferroelectric liquidcrystal; and

b) a driving means including a first drive means for applying a scanningselection signal two or more scanning electrodes apart in one verticalscanning so as to effect one picture scanning in plural times ofvertical scanning, and so that the scanning selection signal is appliedto scanning electrodes which are not adjacent to each other in at leasttwo consecutive times of vertical scanning, and a second drive means forapplying data signals in synchronism with the scanning selection signal.

According to a third aspect of the present invention, there is provideda liquid crystal apparatus comprising:

a) a liquid crystal device comprising an electrode matrix composed ofscanning electrodes and data electrodes, and a ferroelectric liquidcrystal, and

b) a driving means including a scanning drive means and a data drivemeans;

said scanning drive means including: (i) means for applying to thescanning electrodes a first scanning selection signal and a secondscanning selection signal having mutually different voltage waveforms inone vertical scanning period, and (ii) means for selecting scanningelectrodes N scanning electrodes apart in a first vertical scanningperiod and selecting scanning electrodes not selected in the firstvertical scanning period N scanning electrodes apart (N is an integersuch as 1, 2, 3, . . . ) in a second vertical scanning period so thateach scanning electrode is supplied with the first and second scanningselection signals in a frame period including at least the first andsecond vertical scanning periods;

said data drive means being a means for applying data signals insynchronism with the scanning selection signals.

According to a fourth aspect of the present invention, there is provideda liquid crystal apparatus comprising:

a) a liquid crystal device comprising an electrode matrix composed ofscanning electrodes and data electrodes, and a ferroelectric liquidcrystal; and

b) a driving means including:

a first drive means for applying a scanning selection signal two or morescanning electrodes apart in one vertical scanning so as to effect onepicture scanning in plural times of vertical scanning, said scanningselection signal comprising a former voltage of one polarity and alatter voltage of the other polarity with respect to the voltage levelof a non-selected scanning electrode; and

a second drive means for applying to all or a prescribed part of thedata electrodes a voltage signal providing a voltage for causing oneorientation state of the ferroelectric liquid crystal in combinationwith said former voltage of one polarity of the scanning selectionsignal, and applying to a selected data electrode among said all or aprescribed part of the data electrodes a voltage signal providing avoltage for causing the other orientation state of the ferroelectricliquid crystal and to the other data electrodes a voltage signalproviding a voltage not changing the previous state of the ferroelectricliquid crystal, respectively, in combination with the latter voltage ofthe other polarity.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an electrode matrix or matrix electrodestructure of an FLC device used in the present invention;

FIG. 2 is a cross-sectional view taken along the line A--A' of the FLCdevice shown in FIG. 1;

FIG. 3 is an illustration of intermediate gradations;

FIGS. 4A-4E are driving waveform diagrams used in the invention;

FIG. 5 is a schematic illustration of a display state of a matrixelectrode structure;

FIGS. 6A and 6B show a set of driving waveform diagrams used in theinvention, and FIGS. 7A-7C are time charts showing successions of thedriving waveforms;

FIGS. 8A and 8B show another set of driving waveform diagrams used inthe invention, and FIGS. 9A-9C are time charts showing successions ofthe driving waveforms;

FIGS. 10A-10B and 11A-11B respectively show still another set of drivingwaveform diagrams used in the invention;

FIG. 12 is an illustration of a display state on an electrode matrix;

FIGS. 13A, 13B, 14A, 14B, 15A-1, 15A-2, 15B-1 to 15B-4, 16A-1, 16A-2,16B-1 to 16B-4, 17A-1, 17A-2 and 17B-1 to 17B-4 respectively illustratea set of driving waveforms (scanning signals or data signals) accordingto another embodiment of the invention;

FIGS. 18A, 18B, 19A and 19B show a set of driving waveform diagramsaccording to prior art;

FIG. 20 is a schematic illustration of a display state of a displaypanel of the prior art;

FIG. 21A is a test waveform diagram and FIG. 21B is a time chart showingan optical response obtained at that time;

FIGS. 22-27, 28A and 28B respectively show another set of drivingwaveform diagrams used in the invention;

FIG. 29 is a block diagram of a liquid crystal apparatus according tothe invention;

FIGS. 30 and 31 are schematic perspective views for explaining operationprinciple of a ferroelectric liquid crystal device used in theinvention; and

FIG. 32 is a driving waveform diagram outside the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be explained based on an embodimentapplicable to a ferroelectric liquid crystal (FLC).

FIG. 1 is a schematic plan view of a matrix electrode structure of anFLC device according to an embodiment of the present invention and FIG.2 is a cross-sectional view taken along the line A--A' in FIG. 1.Referring to these figures, the FLC device comprises upper electrodes11A (A₁, A₂, A₃, . . . ) and 11B (B₁, B₂, B₃, B₄, . . . ) constitutingdata electrodes, and lower electrodes 12 constituting scanningelectrodes C (C₀, C₁, C₂, C₃, . . . ). These data electrodes 11A, 11Band scanning electrodes 12 are formed on glass substrates 13 and 14,respectively, and mutually arranged so as to form a matrix with an FLCmaterial 15 disposed therebetween. As shown in the figures, one pixel isconstituted by a region E surrounded by a dashed line, i.e., a regionwhere a scanning electrode C (C₂ is shown as an example) and two dataelectrodes A (A₂) and B (B₂) (electrode width: A>B). In this instance,the width of each data electrode A is wider than an accompanying dataelectrode B. The scanning electrodes C and the data electrodes A, B arerespectively connected to a power supply (not shown) through switches SW(or equivalents thereof). The switches SW are also connected to acontroller unit (not shown) for controlling the ON/OFF of the switches.Based on this arrangement, a gray scale display in the pixel E, forexample, composed of the scanning electrode C₂ and the data electrodes Aand B, may be effected under the control by means of the controllercircuit as follows. When the scanning electrode C₂ is selected orscanned, a white display state ("W") is given by applying a "W" signalto the data electrodes A₂ and B₂ respectively; a display state of "Gray1" is given by applying a "W" signal to A₂ and a black ("B") signal toB₂ ; a display state of "Gray 2" is given by applying a "B" signal to A₂and a "W" signal to B₂ ; and a black display state ("B") is given byapplying a "B" signal to A₂ and B₂ respectively. FIG. 3 shows theresultant states W, Gray 1, Gray 2 and B constituting a gray scale.

In this way, a gray scale of 4 levels can be realized by using FLC whichper se is essentially capable of only a binary expression.

In a preferred embodiment of the present invention, a pixel E iscomposed of a plural number (n) of intersections of electrodes havingintersection areas giving a geometric series of ratios such as 1:2:4:8:. . . :2^(n-1) (the minimum intersection area is taken as 1 (unit).

In the present invention, if a scanning electrode is divided into twoelectrode stripes having widths C and D and combined with the dataelectrodes A and B (A≠B), 8 gradation levels can be provided when C=Dand 16 gradation levels can be provided when C≠D.

Further, in case where only the data electrode side is split intoelectrodes A and B, if their widths are set to be equal (A=B) and colorfilters in complementary colors are disposed on the electrodes A and B,a color display of four colors may be possible. For example, if acomplementary color relationship of A=yellow and B=blue or A=magenta andB=green is satisfied, display of four colors of white, black, A's colorand B's color becomes possible.

Referring to FIG. 2, the polarizers 16A and 16B are disposed to havetheir polarization axes intersecting each other, and the intersectingpolarization axes may preferably be disposed to provide a dark state inan erasure phase which will be explained hereinafter.

The electrode matrix shown in FIG. 1 may be driven according to adriving method as will be described hereinbelow.

In the present invention, a scanning selection signal is sequentiallyapplied to the scanning electrodes two or more scanning electrodes apartor every third or more electrode so as to effectively suppress theoccurrence of flickering in scanning drive at a low frame frequency.Particularly, by selecting every fourth or more scanning electrode in afield so that adjacent scanning electrodes are not selected in at leasttwo consecutive fields, the occurrence of flickering can be suppressedin scanning drive at an even lower frequency. Some embodiments of thismode will be explained with reference to FIGS. 4 and 15-17.

FIGS. 4A-4E show driving waveforms used in the present invention. Morespecifically, FIG. 4A shows a scanning selection signal S_(S), ascanning non-selection signal S_(N), a white data signal I_(W) and ablack data signal I_(B). When a pixel on a selected scanning electrodeto which a scanning selection signal is applied is supplied with a whitedata signal I_(W) through a data electrode, the pixel is erased into adark state (black) in phase T₁ as a result of application of a voltageV₂ at phase t₁ and a voltage V₂ +V₃ at phase t₂, and is then written inai bright state (white) at a subsequently phase t₃ by application of avoltage -(V₁ +V₃). On the other hand, when a pixel on the selectedscanning electrode is supplied with a black data signal I_(B) through adata electrode, the pixel is erased into a black state in phase T₁ as aresult of application of V₂ at phase t₁ and V₂ -V₃ at phase t₂, and theblack state is retained after application of V₃ -V₁, whereby the pixelis written in the black state.

In this embodiment, the above-mentioned scanning selection signal isapplied to the scanning electrodes according to interlaced scanning oftwo or more scanning electrodes apart. FIG. 4B shows an example wherethe scanning selection signal is applied two scanning electrodes apart,i.e., every third scanning electrode. FIG. 4C shows an example set ofdriving waveforms whereby a display state shown in FIG. 5 is obtained.In FIG. 5, • denotes a black written state and ∘ denotes a white writtenstate. In the example shown in FIG. 5, each intersection of scanningelectrodes S₁ -S₉ and a data electrodes I₁ is set to have an area (pixelarea) which is twice that of each intersection of the scanningelectrodes S₁ -S₉ and a data electrode I₂ to form pixels P₁ -₉. Asdescribed above, the pixels P₁ -P₄ display four gradation levels due todifferences in proportions of black and white states.

In the above example, scanning electrodes have been selected byinterlaced scanning of two scanning electrodes apart. In addition to theabove, however, selection or interlaced scanning of scanning electrodescan be effected three, four, . . . or N electrodes apart.

When the selection is effected N lines apart, one frame scanning mayinclude N+1 fields of scanning. In the present invention, an interlacedscanning system of 8 or more lines apart may be effective forsuppressing the flickering.

Further preferred embodiments are shown in FIGS. 4D and 4E. In anembodiment shown in FIG. 4D, a scanning selection signal is applied tothe scanning electrodes 6 scanning electrodes apart (the number ofscanning fields F=7), so that the scanning selection signal is appliedto the 1st (F+1-th . . . ), 5th (F+5-th . . . ), 3rd (F+3-th . . . ),7th (F+7-th . . . ), 2nd (F+2-th . . . ), 6th (F+6-th . . . ) and 4th(F+4-th . . . ) scanning electrodes in the 1st, 2nd, . . . , and 7thfields, respectively. Thus, the order of scanning electrodes to whichthe scanning selection signal is applied sequentially does notcorrespond to the order of field. In other words, in the driving schemeshown in FIG. 4D, between any consecutive two of the seven fieldsconstituting one frame (picture) scanning, the scanning selection signalis applied to scanning electrodes which are not adjacent to each other.

FIG. 4E shows another embodiment of the above scheme (interlacedscanning of 3 lines apart). The driving scheme adopted is theembodiments of FIGS. 4D and 4E is more effective in suppressing theoccurrence of flickering than in the scanning signal application schemeshown in FIG. 4B.

FIGS. 6-14 show interlaced scanning schemes wherein a scanning selectionsignal is selectively applied to every other scanning electrode.

FIGS. 6A and 6B show a set of driving waveforms used in the presentinvention. More specifically, FIG. 6A shows a scanning selection signalS_(4n-3) (n=1, 2, 3, . . . ) applied to a (4n-3)th scanning electrode, ascanning selection signal S_(4n-2) applied to a (4n-2)th scanningelectrode, a scanning selection signal S_(4n-1) applied to a (4n-1)thscanning electrode and a scanning selection signal applied to a 4n-thscanning electrode which are respectively applied in a (4M-3)th fieldF_(4M-3), a (4M-2)th field F_(4M-2), a (4M-1)th field F_(4M-1) and a4Mth field F_(4M) (M=1, 2, 3 . . . ). Herein, one field means onevertical scanning operation or period). According to FIG. 6A, thescanning selection signal S_(4n-3) has voltage polarities (with respectto the voltage level of a scanning non-selection signal) which areopposite to each other in the corresponding phases of the (4M-3)th fieldF_(4M-3) and (4M-1)th field F_(4M-1), while the scanning selectionsignal S_(4n-3) is so composed as to effect no scanning i.e. so as to bea scanning non-selection signal, in the (4M-2)th field F_(4M-2) or 4Mthfield F_(4M). The scanning selection signal S_(4n-1) is similar, but thescanning selection signal S_(4n-3) and S_(4n-1) applied in one fieldperiod have different voltage waveforms and have mutually oppositevoltage polarities in the corresponding phases.

Similarly, the scanning selection signal S_(4n-2) has voltage polarities(with respect to the voltage level of the scanning non-selection signal)which are mutually opposite in the corresponding phases of the (4M-2)thfield F_(4M-2) and 4Mth field F_(4M) and effects no scan in the (4M-3)thfield F_(4M-3) or (4M-1)th field F_(4M-1). The scanning selection signalS_(4n) is similar, but the scanning selection signals S_(4n-2) andS_(4n) applied in one field period have different voltage waveforms andhave mutually opposite voltage polarities in the corresponding phases.

Further, in the driving waveform embodiment shown in FIGS. 6A and 6B, athird phase is disposed for providing a pause to the whole picture(e.g., by applying a voltage of 0 simultaneously to all the pixelsconstituting the picture), and for this purpose, the scanning selectionsignals are set to have a voltage of zero (the same voltage level as thescanning non-selection signal).

Referring to FIG. 6B, data signals applied to data electrodes in the(4M-3)th field F_(4M-3) comprise a white signal (one for providing avoltage 3V₀ exceeding a threshold voltage of the FLC at the second phasein combination with the scanning selection signal S_(4n-3) to form awhite pixel) and a hold signal (one for applying to a pixel a voltage±V₀ below the threshold voltage of the FLC in combination with thescanning selection signal S_(4n-3)) which are selectively applied insynchronism with the scanning selection signal S_(4n-3) ; and a blacksignal (for providing a voltage -3V₀ exceeding a threshold voltage ofthe FLC at the second phase in combination with the scanning selectionsignal S_(4n-1) to form a black pixel) and a hold signal (for applyingto a pixel a voltage ±V₀ below the threshold voltage of theferroelectric liquid crystal in combination with the scanning selectionsignal S_(4n-1)) which are selectively applied in synchronism with thescanning selection signal S_(4n-1). On the contrary, the (4n-2)thscanning electrode and (4n)th scanning electrode are supplied with ascanning non-selection signal, so that the pixels on these scanningelectrodes are supplied with the data signals as they are.

In the (4M-2)th field F_(4M-2) subsequent to the writing in theabove-mentioned (4M-3)th field F_(4M-3), data signals applied to thedata electrodes comprise the above-mentioned white signal and holdsignal which are selectively applied in synchronism with the scanningselection signal S_(4n-2) ; and the above-mentioned black signal andhold signal which are selectively applied in synchronism with thescanning selection signal S_(4n). On the other hand, the (4n-3)th and(4n-1)th scanning electrodes are supplied with a scanning non-selectionsignal so that the data signals are applied as they are to the pixels onthese scanning electrodes.

In the (4M-1)th field F_(4M-1) subsequent to the writing in theabove-mentioned (4M-2)th field F_(4M-2), data signals applied to thedata electrodes comprise the above-mentioned white signal and holdsignal which are selectively applied in synchronism with the scanningselection signal S_(4n-3) ; and the above-mentioned white signal andhold signal which are selectively applied in synchronism with thescanning selection signal S_(4n-1). On the other hand, the (4n-2)th and(4n)th scanning electrodes are supplied with a scanning non-selectionsignal so that the data signals are applied as they are to the pixels onthese scanning electrodes.

In the 4Mth field F_(4M) subsequent to the writing in theabove-mentioned (4M-1)th field F_(4M-1), data signals applied to thedata electrodes comprise the above-mentioned black signal and holdsignal which are selectively applied in synchronism with the scanningselection signal S_(4n-2) ; and the above-mentioned white signal andhold signal which are selectively applied in synchronism with thescanning selection signal S_(4n). On the other hand, the (4n-3)th and(4n-1)th scanning electrodes are supplied with a scanning non-selectionsignal so that the data signals are applied as they are to the pixels onthese scanning electrodes.

FIGS. 7A, 7B and 7C are time charts showing successions of drivingwaveforms shown in FIGS. 6A and 6B used for writing to form a displaystate shown in FIG. 12. In FIG. 12, ∘ denotes a pixel written in whiteand • denotes a pixel written in black. Further, referring to FIG. 7B,at I₁ -S₁ is shown a time-serial voltage waveform applied to theintersection of a scanning electrode S₁ and a data electrode I₁. At I₂-S₁ is shown a time-serial waveform applied to the intersection of thescanning electrode S₁ and a data electrode I₂. Similarly, at I₁ -S₂ isshown a time-serial voltage waveform applied to the intersection of ascanning electrode S₂ and the data electrode I₁ ; and at I₂ -S₂ is showna time-serial voltage waveform applied to the intersection of thescanning electrode S₂ and the data electrode I₂.

A gradational display may be effected by applying the embodiment ofFIGS. 6A and 6B as well as one shown in FIGS. 8A and 8B explainedhereinbelow to an electrode matrix as shown in FIG. 1.

FIGS. 8A and 8B show another set of driving waveforms used in thepresent invention. In the driving embodiment shown in FIGS. 8A and 8B,each of the scanning selection signals S_(4n-3) and S_(4n-1) comprisestwo voltage waveforms which are of mutually opposite polarities withrespect to the voltage level of a scanning non-selection signal, andeach of the scanning selection signals comprises a former pulse and alatter pulse, the former having a duration twice that of the latter.Further, each data signal is characterized by having a voltage of zeroat the first phase and alternating voltages at the first and thirdphases which are of mutually opposite polarities with respect to thescanning non-selection signal voltage. FIGS. 9A-9C are time chartsshowing successions of driving waveforms shown in FIGS. 8A and 8B usedfor writing to form the display state shown in FIG. 12.

FIGS. 10 (10A and 10B) and 11 (11A and 11B) respectively show anotherpreferred set of driving waveforms used in the present invention. In theembodiments shown in FIGS. 10 and 11, the scanning selection signals andthe data signals are designed to have two voltage levels so thatdesigning of a driving circuit therefor is simplified.

In the above driving embodiments, the amplitude of a scanning selectionsignal is set to 2|±V₀ |, while the amplitude of a data signal is set to|±V₀ |. In the present invention, however, when the amplitude of ascanning selection signal is denoted by |Sap| and the amplitude of adata signal is denoted by |Iap|, it is generally preferred to satisfy|Iap|/|Sap|≦1, particularly |Iap|/|Sap|<1/1.2.

In the present invention, if an FLC has two threshold voltages V_(th1)and -V_(th2) (V_(th1), V_(th) >0), the above-mentioned voltage V₀ may beset to satisfy the following relationships:

    V.sub.0 <V.sub.th1 <3V.sub.0,

    and

    -3V.sub.0 <-V.sub.th2 <-V.sub.0.

The following Table 1 shows a time relation of a white selection voltageS_(W) for forming white selection pixels and a half-selection voltage Happlied as that time in fields F₁, F₂, F₃, F₄, . . .

                  TABLE 1                                                         ______________________________________                                                     F.sub.1                                                                             F.sub.2 F.sub.3 F.sub.4 . . .                              ______________________________________                                        Scanning line S.sub.1                                                                            S.sub.W       H                                            Scanning line S.sub.2      S.sub.W     H                                      Scanning line S.sub.3                                                                            H             S.sub.W                                      Scanning line S.sub.4      H           S.sub.W                                .                                                                             .                                                                             ______________________________________                                    

The following Table 2 shows another time relation for forming whiteselection pixels.

                  TABLE 2                                                         ______________________________________                                                     F.sub.1                                                                             F.sub.2 F.sub.3 F.sub.4 . . .                              ______________________________________                                        Scanning line S.sub.1                                                                            S.sub.W H     S.sub.W                                                                             H                                      Scanning line S.sub.2                                                                            S.sub.W H     S.sub.W                                                                             H                                      Scanning line S.sub.3                                                                            S.sub.W H     S.sub.W                                                                             H                                      Scanning line S.sub.4                                                                            S.sub.W H     S.sub.W                                                                             H                                      .                                                                             .                                                                             ______________________________________                                    

According to Table 1 relating to the invention, in (4M-3)th fields F₁,F₅, . . . , a white selection voltage S_(W) is applied to pixels (whiteselection pixels) on (4N-3)th scanning lines S₁, S₅, . . . , ahalf-selection voltage is applied to pixels (white selection pixels) on(4N-1)th scanning lines S₃, S₇, . . . , and the pixels on (4N-2)th and(4N)th scanning electrodes S₂, S₄, S₆, S₈, . . . are not scanned. On thecontrary, according to Table 2, pixels (white selection pixels) on allthe scanning lines are supplied with a white selection voltage in theodd-numbered fields F₁, F₃, . . . , and pixels (white selection pixels)on all the scanning lines are supplied with a half-selection voltage inthe even-numbered fields. As a result, according to the drivingembodiment following the Table 2, flickering occurs at a 1/2 fieldfrequency (In the case of Table 2, the field frequency is equal to theframe frequency because all the scanning lines are scanned in onevertical scanning). This means that, if the frame frequency is taken asan ordinary value of 30 Hz, flickering occurs at 15 Hz. In contrastthereto, according to the method of Table 1, only a half of the totalscanning lines are scanned in one vertical scanning period (one field)so that the field frequency (the reciprocal of one vertical scanningperiod) f₁ can be increased to twice the field frequency f₂ according tothe method of Table 2 (f₁ =f₂). As a result, the flickering occurs at afrequency which is four times that according to the method of Table 2.More specifically, in the case of an ordinary frequency of 30 Hz, theflickering occurs at a frequency of 60 Hz. Moreover, according to themethod of Table 1, the number of pixels supplied with a half-selectionvoltage is reduced to 1/4 of that according to the method of Table 2,whereby the flickering is effectively prevented by that much.

Further, according to a method using a time relation shown in Table 3below, in an odd-numbered field, pixels (white selection pixels) on theodd-numbered scanning lines S₁, S₃, . . . are supplied with a whiteselection voltage and pixels (white selection pixels) on theeven-numbered scanning lines S₂, S₄, . . . are supplied with ahalf-selection voltage so that flickering occurs at the field frequency(equal to the frame frequency because all the scanning lines are scannedin one vertical scanning according to Table 3).

                  TABLE 3                                                         ______________________________________                                                     F.sub.1                                                                             F.sub.2 F.sub.3 F.sub.4 . . .                              ______________________________________                                        Scanning line S.sub.1                                                                            S.sub.W H     S.sub.W                                                                             H                                      Scanning line S.sub.2                                                                            H       S.sub.W                                                                             H     S.sub.W                                Scanning line S.sub.3                                                                            S.sub.W H     S.sub.W                                                                             H                                      Scanning line S.sub.4                                                                            H       S.sub.W                                                                             H     S.sub.W                                .                                                                             .                                                                             ______________________________________                                    

In contrast thereto, according to the method of Table 1 as describedabove, only a half of the total scanning lines are scanned in onevertical scanning period (one field) so that the field frequency f₁ canbe increased to twice the field frequency f₃ according to the method ofTable 3 (f₁ =f₃). As a result, the flickering occurs at a frequencywhich is twice that according to the method of Table 3. Thus, in thecase of an ordinary frequency of 30 Hz, the flickering occurs at afrequency of 60 Hz. Moreover, according to the method of Table 1, thenumber of pixels supplied with a half-selection voltage is reduced to1/2 of that according to the method of Table 3, whereby the flickeringis effectively prevented by that much.

FIGS. 13A and 13B show still another set of driving waveforms used inthe present invention.

In the driving embodiment shown in FIG. 6, the scanning selection signalS_(4n-3) applied to the (4n-3)th scanning electrode (or the scanningselection signal S_(4n-1) applied to the (4n-1)th scanning electrode) inthe (4M-3)th field F_(4M-3) and the scanning selection signal S_(4n-2)applied to the (4n-1)th scanning electrode (or the scanning selectionsignal S_(4n) applied to the 4n-th scanning electrode) in the (4M-2)thfield F_(4M-2) are the same. In contrast thereto, in the drivingembodiment shown in FIG. 13(13A and 13B), S_(4n-3) (or S_(4n-1)) inF_(4M-3) and S_(4n-2) (or S_(4n)) in F_(4M-2) have mutually differentvoltage waveforms and have mutually opposite voltage polarities in thecorresponding phases.

The following Table 4 shows a time relation of a white selection voltageS_(W) for forming white selection pixels and a half-selection voltage Happlied at that time in fields F₁, F₂, F₃, F₄ . . . according to thedriving embodiment shown in FIG. 13.

                  TABLE 4                                                         ______________________________________                                                     F.sub.1                                                                             F.sub.2 F.sub.3 F.sub.4 . . .                              ______________________________________                                        Scanning line S.sub.1                                                                            S.sub.W       H                                            Scanning line S.sub.2      H           S.sub.W                                Scanning line S.sub.3                                                                            H             S.sub.W                                      Scanning line S.sub.4      S.sub.W     H                                      .                                                                             .                                                                             ______________________________________                                    

As is apparent from a comparison between Tables 1 and 4, the drivingembodiment of FIG. 13 is effective for preventing flickering similarlyas the embodiment shown in FIG. 6 except that the time relation betweenthe application of a white-selection voltage S_(W) and that of ahalf-section voltage in fields F₁, F₂, F₃, F₄, . . . are different fromthose shown in FIG. 6. Thus, the present invention is not limited to aparticular time relation according to which a selection voltage and ahalf-selection voltage are applied in each field.

FIGS. 14A and 14B show a further set of driving waveforms used in thepresent invention. In the embodiment shown in FIG. 6 (or FIG. 13), thetime for applying a selection voltage is shifted to a next (orpreceding) scanning line for each field as is understood from Table 1(or Table 4). More specifically, if it is assumed that a scanning lineSn is selected in an n-th field, a scanning line S_(n+1) (or S_(n-1)) isselected in an (n+1)th field and a scanning line S_(n+2) (or S_(n-2)) isselected in an (n+2)th field. In this way, the time for applying aselection voltage is shifted sequentially for each field. For thisreason, in case where a contrast (brightness difference) is presentbetween a selection time and a half-selection time, the contrast occursat the time of applying a selection voltage to a scanning line and issequentially moved on a screen like a line flow to result in aremarkable degradation in display quality.

Table 5 below shows a time relation for application of a white selectionvoltage S_(W) and a half-selection voltage H at that time applied topixels in fields F₁, F₂, F₃, F₄, . . . by using the driving embodimentshown in FIGS. 14 (14A and 14B).

                  TABLE 5                                                         ______________________________________                                         ##STR1##                                                                      ##STR2##                                                                     ______________________________________                                    

The driving embodiment shown in FIGS. 14A and 14B has been designed toremove a problem caused accompanying a time relation of applyingselection voltages. Thus, as will be apparent from the above Table 5,the sequential movement of a point of applying a selection voltage inone direction is prevented to the utmost while avoiding degradation indisplay quality.

Thus, the present invention also provides a solution to a problem causedby a time relation of applying a selection voltage and a half-selectionvoltage in each field.

FIGS. 15A and 15B show still another driving embodiment of the presentinvention. In the embodiment of FIG. 6, the number of scanning linesscanned in one vertical scanning period is 1/2 of the total scanninglines and all the scanning lines are scanned in two times of verticalscanning. In the embodiment of FIGS. 15A and 15B, every fourth scanningline is scanned in one vertical scanning period, and a scanning linenext to the one scanned in the previous vertical scanning period isscanned in the next vertical scanning period. Accordingly, the number ofscanning lines scanned in one vertical scanning period is 1/4 of thetotal scanning lines, so that all the scanning lines are scanned in fourtimes of vertical scanning.

Table 6 below shows a time relation for application of a white selectionvoltage S_(W) and a half-selection voltage H applied to pixels in fieldsF₁, F₂, F₃, F₄, . . . by using the driving embodiment shown in FIGS. 15(15A and 15B).

                  TABLE 6                                                         ______________________________________                                                 F.sub.1                                                                            F.sub.2                                                                             F.sub.3                                                                              F.sub.4                                                                           F.sub.5                                                                            F.sub.6                                                                           F.sub.7                                                                            F.sub.8 . .                      ______________________________________                                                                                     .                                Scanning lines S.sub.1                                                                   S.sub.W               H                                            Scanning lines S.sub.2                                                                          S.sub.W             H                                       Scanning lines S.sub.3  S.sub.W           H                                   Scanning lines S.sub.4       S.sub.W           H                              Scanning lines S.sub.5                                                                   H                     S.sub.W                                      Scanning lines S.sub.6                                                                          H                   S.sub.W                                 Scanning lines S.sub.7  H                 S.sub.W                             Scanning lines S.sub.8       H                 S.sub.W                        .                                                                             .                                                                             ______________________________________                                    

As is shown in Table 6 in comparison with Table 1, in (8M-7)th fieldsF₁, F₉, . . . in the embodiment of FIG. 15, pixels (white selectionpixels) on (8M-7)th scanning lines S₁, S₉, . . . are supplied with awhite selection voltage; pixels (white selection pixels) on (8M-3)thscanning lines S₅, S₁₃, . . . are supplied with a half-selectionvoltage; and pixels on (8N-6)th , (8N-5)th, (8N-4)th, (8N-2)th, (8N-1)thand (8N)th scanning lines S₂, S₃, S₄, S₆, S₇, S₈ . . . are not scanned.As a result, in the driving embodiment of FIG. 15, only 1/4 of the totalscanning lines are scanned in one vertical scanning period (one field),so that the field frequency f₁₀ (the reciprocal of one vertical scanningperiod) becomes two times the field frequency f₁ according to Table 1(f₁₀₌ 2f₁). Thus, in the case of an ordinary frame frequency of 30 Hz,the flickering occurs at a frequency of 120 Hz. In this way, even if thenumber of scanning lines is increased for providing a larger screen,flickering can be effectively suppressed. Moreover, according to theembodiment of FIG. 15, the number of pixels supplied with ahalf-selection voltage is reduced to 1/2 of that according to theembodiment of Table 1 (FIG. 6), whereby the flickering is furthereffectively prevented.

As described above, in the present invention, all the scanning lines arenot scanned in one time of vertical scanning but in several times ofvertical scanning so as to prevent flickering. Thus, the number ofvertical scanning required for vertical scanning is not particularlylimited as far as it is at least two times.

FIGS. 16A and 16B show still another driving embodiment of the presentinvention. In the embodiment shown in FIG. 15, (8N-7)th and (8N-3) thscanning lines are scanned in an (8M-7)th field, and (8N-6)th and(8N-2)th scanning lines are scanned in the subsequent (8M-6)th field. Inother words, a scanning line next to the one scanned in a previous fieldis scanned in the next field, a further next scanning line is scanned inthe subsequent field, and so on. In such a scanning method, as isapparent from Table 6, the time or point for applying a selectionvoltage is shifted sequentially for each field. As a result, in casewhere a contrast is present between a selection time and ahalf-selection time, the constrast occurs at the time of applying aselection voltage to a scanning line and is sequentially moved on ascreen like a line flow to result in a remarkable degradation is displayquality.

Table 7 below shows a time relation for application of a white selectionvoltage S_(W) and a half-selection voltage H at that time applied topixels in fields F₁, F₂, F₃, F₄, ... By using the driving eembodimentshown in FIG. 16 (16A and 16B).

                  TABLE 7                                                         ______________________________________                                                  F.sub.1                                                                           F.sub.2                                                                              F.sub.3                                                                             F.sub.4                                                                            F.sub.5                                                                           F.sub.6                                                                            F.sub.7                                                                           F.sub.8 . .                      ______________________________________                                                                                     .                                Scanning lines S.sub.1                                                                    S.sub.W               H                                           Scanning lines S.sub.2   S.sub.W           H                                  Scanning lines S.sub.3                                                                          S.sub.W             H                                       Scanning lines S.sub.4       S.sub.W           H                              Scanning lines S.sub.5                                                                    H                     S.sub.W                                     Scanning lines S.sub.6   H                 S.sub.W                            Scanning lines S.sub.7                                                                          H                   S.sub.W                                 Scanning lines S.sub.8       H                 S.sub.W                        .                                                                             .                                                                             ______________________________________                                    

The driving embodiment shown in FIG. 16A and 16B has been designed toremove a problem as described above accompanying a time relation ofapplying selection voltages. Thus, as will be apparent from the aboveTable 7, the sequential movement of a point of applying a selectionvoltage in one direction is prevented to the utmost while accordingdegradation in display quality

FIG. 17 (17A and 17B) shows still another preferred driving embodimentof the present invention. As shown in FIG. 17A-1 and 17A-2, a scanningselection signal is applied to every fourth scanning electrode in afield, and the scanning electrodes selected in two consecutive fieldsare not adjacent to each other.

In the present invention, all the scanning lines are scanned in at leasttwo times of vertical scanning to prevent the occurrence of flickering,and the order of scanning scanning lines is not limited. Further, in thepresent invention, in addition to the above embodiment, a scanningselection signal may also be applied plural (A) lines apart (A=2, 3, 5,.., 20), and the vertical scanning may be repeated (A+1) times.

In the present invention, in addition to the above-described drivingwaveforms, there may be used those unit driving waveforms utilized inmultiplex driving systems as disclosed in U.S. Pat. Nos. 4,548,476;4,655,561; 4,638,310; 4,705,345; "SID 85 Digest" (1985) p.p. 131-134 "AnApplication of Chiral Smectic-C Liquid Crystal to a multiplexed Large-Area Display". Particularly, the above "SID 85 Digest" discloses theuse of two bipolar voltages of mutually anti-phases, which has beenfound to accompany the following features.

FIG. 18A shows driving waveforms used in an odd-numbered frame, and FIG.18B shows driving waveforms used in an even-numbered frame. Referring toFIG. 18A, at (a) is shown a scanning selection signal, at (b) is shown ascanning non-selection signal, and at (c) and (d) are shown data signalscomprising two bipolar voltages of mutually antiphases. In theodd-numbered frame, the data signal at (c) functions as a hold signal(H.S.), and the data signal at (d) functions as a white (or black)writing signal. In the even-numbered frame, the data signal at (c)functions as a black (or white) writing signal, and the data signal at(d) functions as a hold signal.

FIG. 19A shows a driving waveform applied to a certain noted pixel(formed at an intersection of a scanning electrode and a data electrode)the time of non-selection when supplied with "white (or black)" - "hold"signals, and FIG. 19B shows a driving waveform applied to such a pixelwhen supplied with "black (or white" - "hold" signals. As shown in FIG.19A and 19B, when a unit pulse duration is denoted by ΔT, a certainnoted pixel at the time of non-selection is supplied with a pulsecomponent of 2ΔT duration.

A display of a white image on a black background was formed whileapplying a scanning selection signals periodically and repeatedly to thescanning electrodes. A display obtained at that time is schematicallyshown in FIG. 20. Referring to FIG. 20, a display panel 201 has ascanning electrode side 202 and a data electrode side 203, on the panel201 are formed a black background, white image portions 205a and paleblack or gray background portions 205b As is understood from such adisplay state of the display panel 201, gray or pale black backgroundportions were formed at regions expected to form a part of the blackbackground along the data electrodes providing the white image portions.Such a display state degrades the display quality and is not desirable.

In order to find the cause of the above phenomena, a driving waveformshown in FIG. 21A was applied to an intersection P₁ of a scanningelectrode S_(n) and a data electrode I shown in FIG. 20. At this time,the data electrode I was supplied with data signals of B→B→B→B→W→W→ (B:black, W: white) in synchronism with the scanning signals applied to thescanning electrodes S_(n), S_(n+1), S_(n+2), S_(n+3), S_(n+4), S_(n+5)and S_(n+6). FIG. 21B shows an optical response obtained at that timemeasured by a photomultiplier. As is understood from FIG. 21A, theintersection P₁ was supplied with a pulse with a duration of 2ΔT at thetime of switching of data signals from B→W, which caused an opticalfluctuation 211 as shown in FIG. 21B. Accordingly, such an optical"fluctuation" was cased based on occurrence of pale black backgroundportions. The above phenomenon was remarkably observed particularly in arefresh drive scheme wherein a scanning selection signal wasperiodically applied.

According to the present invention, however, such an optical fluctuationhas been effectively suppressed by using a liquid crystal apparatuscomprising a) a liquid crystal device comprising an electrode matrixcomposed of scanning electrodes an data electrodes, and a ferroelectricliquid crystal; and b) a driving means including: a first means forselecting at least one scanning electrode and applying to the selectedat least one scanning electrode a scanning selection signal whichcomprises a pulse of one polarity and a pulse of the the other polaritywith respect to the voltage level of a non-selected scanning electrode,said pulses of one and the other polarities having mutually differentpulse durations, and a second means for applying data signals to thedata electrode, each data signal comprising a pulse of one polarity anda pulse of the other polarity with respect to the voltage level of anon-selected scanning electrode, the pulses of one and the otherpolarities having mutually different pulse durations, a pulse having thelargest pulse duration of the pulses being synchronized with the pulseat the last phase of the scanning selection signal.

FIGS. 22-28 show driving waveforms used in the present invention forsuppressing the above-mentioned "fluctuation".

In the driving embodiment shown in FIG. 22, an odd-numbered scanningelectrode is supplied with a scanning selection signal S_(2n-1) (n=1, 2,3, ...). in an odd-numbered frame F_(2M-1) (M=1, 2, 3, ...). The signalS_(2n-1) comprises a voltage -V_(S) (with respect to the voltage of ascanning non-selection signal) at a first phase t₁, a voltage V_(S) at asecond phase t₂ and a voltage O at a final phase t₃. The pulse durationof the voltage V_(S) at phase t₂ is set to be at least twice, preferablytwice, the pulse duration of the voltage -V_(S) at phase t₁. Further, aneven-numbered scanning electrode is supplied with a scanningnon-selection signal S_(2n) (n=1, 2, 3, ...) in an odd-numbered frameF_(2M-1) (M=1, 2, 3, ...). The signal S_(2n) comprises voltages ofopposite polarities to those of the scanning selection signal S_(2n-1)at phases t₁ and t₂, respectively.

On the other hand, in an even-numbered frame F_(2M) (M=1, 2, 3, ...), anscanning non-selection signal S_(2n-1) applied o an odd-number scanningelectrode has the same waveform as the scanning selection signal S_(2n)applied in the odd-numbered frame F_(2M-1), and an scanningnon-selection signal S_(2n) applied to an even-numbered scanningelectrode has the same waveform as the scanning selection signalS_(2n-1) applied in the odd-numbered frame F_(2M-1).

In synchronism with the above scanning selection signals, the datalectrodes are selectively supplied with a white signal, a black signalor a hold signal. The white signal comprises a voltage V_(D)synchronized at phase t₁, a voltage -V_(D) synchronized at phase t₂ anda voltage V_(D) synchronized at phase t₃. Accordingly, the pulseduration of the voltage -V_(D) at phase t₂ of the white signal islikewise set to be at least twice, preferably twice, the pulse durationof thee voltage V_(D) at the first phase t₁. Further, of the datasignals, the black signal comprises voltages of opposite polarities tothose of the white singal at phases t₁, t₂ and t₃, respectively.

In the odd frame F_(2M-1), a hold signal synchronized with the scanningselection signal S_(2n-1) is set to have the same waveform as theabove-mentioned black signal, and a hold signal synchronized with thescanning selection signal S_(2n) is set to have the same waveform as theabove-mentioned white signal.

Further, in the even frame F_(2M), a hold signal synchronized with thescanning selection signal S_(2n-1) is set to have the same waveform asthe white signal, and a hold signal synchronized with the scanningselection signal S_(2n) is set to have the same waveform as the blacksignal.

In the driving embodiment shown in FIG. 22, the maximum duration (Tb) ofa single polarity voltage applied to a pixel at the time ofnon-selection is Δt so that it has become possible to solve the problemcaused in the prior art embodiment where the maximum duration has been2Δt.

FIG. 23 shows a driving embodiment which is a modification of the oneshown in FIG. 22. In the eembodiment shown in FIG. 23, scanningselection signals S_(2n-1) and S_(2n) are respectively set to havevoltages of V_(S) (or -V_(S)) and -V_(S) (or V_(S)) of mutually oppositepolarities at a first phase t₁, and a second phase t₂ and are both setto have a voltage of zero at a last phase t₃. The signals are set tohave a pulse duration of Δt at phase t₂ and a pulse duration of 3/2·Δtat phase t₁, and the voltage O is set to have a duration of Δt/2.

A white signal, a black signal and a hold signal comprise voltages V_(D)and -V_(D) of mutually opposite polarities applied in synchronism withphase t₁ of the scanning selection signals S_(2n-1) and S_(2n). Of thesevoltages, a frist applied voltage V_(D) or -V_(D) is set to have a pulseduration Δt/2 and a next applied voltage -V_(D) or V_(D) is set to havea duration Δt. Further, at phases t₂ and t₃, the white signal, blacksignal and hold signal comprise a voltage V_(D) or -V_(D) with a pulseduration Δt and a voltage -V_(D) or V_(D) with a pulse duration Δt/2.

In the driving embodiment shown in FIG. 23, the maximum duration Tb of asingle polarity applied to a pixel at the time of non-selection is alsosuppressed to Δt.

In the embodiment shown in FIGS. 24-28, the maximum duration Tb of asingle polarity applied to a pixel at the time of non-selection issuppressed to Δt, so that the above-mentioned problem of "fluctuation"caused in prior art multiplex driving can be solved.

Incidentally, the above-mentioned Δt has been set equal to the maximumduration (time) of voltages V_(D) and -V_(D) used in the data signals.

In the present invention, various types of ferroelectric liquid crystaldevices can be used, including an SSFLC device as disclosed by Clark etal in U.S. Pat. No. 4,367,924, etc., a ferroelectric liquid crystaldevice having an alignment with a remaining helical texture as disclosedby Isogai, et al in U.S. Pat. No. 4,586,791, and a ferroelectric liquidcrystal device having an alignment state as disclosed in G.B. Laid-OpenPatent Application GB-A 2,159,635. The ferroelectric liquid crystaldevice disclosed in GB-A 2,159,635 includes an alignment state providinga tilt angle (an angle between an average molecular axis direction ofliquid crystal molecules and uniaxial orientation axis such as a rubbingaxis) under no electric field which is smaller than that under theapplication of an electric field.

In the present invention, it is possible to use a ferroelectric liquidcrystal having a positive or negative dielectric anisotropy.Particularly, in the case of a device using a ferroelectric liquidcrystal having a negative dielectric anisotropy, it is preferred toapply an AC voltage at a high frequency (e.g., 10 kHz or higher) topixels under non-selection. Such AC application methods are disclosedin, e.g., Japanese Laid-Open Patent Applications JP-A 61-249025,61-249024, 61-246724, 61-246723, 61-246722, and 61-245142.

In FIGS. 22-28A, there have been disclosed driving embodiments whereinthe polarity of the scanning selection signal is inverted for each frameand for each line. It is however possible to adopt an embodiment whereinthe polarity of the scanning selection signal is inverted only for eachframe or inverted every second or fourth frame scanning.

In the present invention, it is further possible not to use the polarityinversion of a scanning selection signal. FIG. 28B shows such a drivingembodiment. In the embodiment shown in FIG. 28B, at the time of scanningone line, all the pixels on the one line are erased in phases t₁ and t₂,and the pixels on the one line is selected into either white or black.In this instance, in the erasure in the phases t₁ and t₂ of the presentinvention, it is preferred to erase the pixels into black. For thispurpose, it is ordinary to dispose a polarization axis in parallel withthe molecular axis of the liquid crystal at the pixels oriented as aresult of the application of the voltages in the phases t₁ and t₂.Alternatively, it is also possible to set the angle between the uniaxialorientation axis and a polarization axis to an angle which is smallerthan the maximum tilt angle under the application of the erasurevoltage. If the pixels are erased into a black (dark) state, littleflushing into a white (bright) state is encountered so that a driving ata relatively low frame frequency becomes possible.

Herein, a specific example is shown hereinbelow.

EXAMPLE

A ferroelectric liquid crystal device was composed to have a number ofpixels of 400 (number of scanning electrodes) ×800 (number of dataelectrodes) by using a ferroelectric liquid crystal showing a negativedielectric anisotropy ("CS1017", available from Chisso K.K) which showedthe following phase transition characteristic. ##STR3## wherein therespective symbols denote the following phases. Cryst: crystal phase

SmC*: chiral smectic phase

SmA: smectic A phase

Ch: cholesteric phase

Iso: isotropic phase.

The ferroelectric liquid crystal showed a spontaneous polarization(P_(S)) of 9.0 nC/cm² and disposed in a layer thickness of 1.5 micronbetween a pair of substrates having the above-mentioned scanningelectrodes and data electrodes coated with polyimide films which hadbeen rubbed in parallel with each other.

The ferroelectric liquid crystal device was driven by using drivingwaveforms shown in FIGS. 22-28 wherein the voltages ±V_(S) were set to±18 volts and ±V_(D) were set to ±6 volts, whereby a drive margin ofone-line scanning time and a static pixel contrast C_(R) (transmittancein the bright state/transmittance in the dark state) were measured. Theresults are shown in the following table.

    ______________________________________                                        Example   Drive      One-line scanning                                                                           Contrast                                   No.       waveform   time (μ sec)                                                                             C.sub.R                                    ______________________________________                                        Example 1 FIG. 22    84-96         6.2                                        Example 2 FIG. 23    144-152       4.9                                        Example 3 FIG. 24    202-236       5.1                                        Example 4 FIG. 25    198-250       5.3                                        Example 5 FIG. 26    160-184       5.1                                        Example 6 FIG. 27    164-176       5.1                                        Example 7 FIG. 28    140-162       5.8                                        Comparative                                                                             FIG. 18    102-120       5.8-6.3                                    Example 1                                                                     ______________________________________                                    

In the examples of the present invention, no pale black stripes as shownin FIG. 20 were observed within the drive margins whereby pictures of agood quality were provided. In contrast thereto, in the comparativeexample, the resultant contrast was not constant and stripes wereobserved to provide a picture of a lower quality.

FIG. 29 is a block diagram illustrating a structural arrangement of anembodiment of the display apparatus according to the present invention.A display panel 801 is composed of scanning electrodes 802, dataelectrodes 803 and a ferroelectric liquid crystal disposed therebetween.The orientation of the ferroelectric liquid crystal is controlled by anelectric field at each intersection of the scanning electrodes and dataelectrodes formed due to voltages applied across the electrodes.

The display apparatus includes a data electrode driver circuit 804,which in turn comprises an image data shift register 8041 for storingimage data serially supplied from a data signal line 806, a line memory8042 for storing image data supplied in parallel from the image datashift register 8041, a data electrode driver 8043 for supplying voltagesto data electrodes 803 according to the image data stored in the linememory 8042, and a data side power supply changeover unit 8044 forchanging over among voltages V_(D), 0 and -V_(D) supplied to the dataelectrodes 803 based on a signal from a changeover control line 811.

The display apparatus further includes a scanning electrode drivercircuit 805, which in turn comprises a decoder 8051 for designating ascanning electrode among all the scanning electrodes based on a signalreceived from a scanning address data line 807, a scanning electrodedriver 8052 for applying voltages to the scanning electrodes 802 basedon a signal from the decoder 8051, and a scanning side power supplychangeover unit 8053 for changing over among voltages V_(S), 0 and-V_(S) supplied to the scanning electrodes 802 based on a signal from achangeover control line 811.

The display apparatus further includes a CPU 808, which receives clockpulses from an oscillator 809, controls the image memory 810, andcontrols the signal transfer over the data signal line 806, scanningaddress data line 807 and changeover control line 811.

As the ferroelectric liquid crystal showing bistability used in thepresent invention, chiral smectic liquid crystals havingferroelectricity are most preferred. Among these liquid crystals, aliquid crystal in chiral smectic C phase (SmC*) or H phase (SmH*) isparticularly suited. These ferroelectric liquid crystals are describedin, e.g., "LE JOURNAL DE PHYSIQUE LETTERS" 36 (L-69), 1975"Ferroelectric Liquid Crystals"; "Applied Physics Letters" 36 (11) 1980,"Submicro-Second Bistable Electrooptic Switching in Liquid Crystals";"Kotai Butsuri (Solid State Physics)" 16 (141), 1981 "Liquid Crystal";U.S. Pat. Nos. 4,556,727, 4,561,726, 4,614,609, 4,589,996 and 4,592,858.Ferroelectric liquid crystals disclosed in these publications may beused in the present invention.

More particularly, examples of ferroelectric liquid crystal compoundused in the present invention aredecyloxybenzylidene-p'-amino-2-methylbutylcinnamate (DOBAMBC),hexyloxybenzylidene-p'-amino-2-chloropropylcinnamate (HOBACPC),4-O-(2-methyl)-butylresorcilidene-4'-octylaniline (MBRA 8), etc.

When a device is constituted by using these materials, the device may besupported with a block of copper, etc. in which a heater is embedded inorder to realize a temperature condition where the liquid crystalcompounds assume an SmC*-or SmH*-phase.

Further, in the present invention, it is possible to use a ferroelectricliquid crystal in chiral smectic F phase, I phase, G phase or K phase inaddition to the above mentioned SmC* and SmH* phases.

Referring to FIG. 30, there is schematically shown an example of aferroelectric liquid crystal cell. Reference numerals 301a and 301bdenote substrates (glass plates) on which a transparent electrode of,e.g., In₂ O₃, SnO₂, ITO (Indium-Tin-Oxide), etc., is disposed,respectively. A liquid crystal of an SmC*-phase in which liquid crystalmolecular layers 302 are oriented perpendicular to surfaces of the glassplates is hermetically disposed therebetween. A full line 303 showsliquid crystal molecules. Each liquid crystal molecule 303 has a dipolemoment (P⊥) 304 in a direction perpendicular to the axis thereof. When avoltage higher than a certain threshold level is applied betweenelectrodes formed on the base plates 301a and 301b, a helical or spiralstructure of the liquid crystal molecule 303 is unwound or released tochange the alignment direction of respective liquid crystal molecules303 so that the dipole moment (P⊥) 304 are all directed in the directionof the electric field. The liquid crystal molecules 303 have anelongated shape and show refractive anisotropy between the long axis andthe short axis thereof. Accordingly, it is easily understood that when,for instance, polarizers arranged in a cross nicol relationship, i.e.,with their polarizing directions crossing each other, are disposed onthe upper and the lower surfaces of the glass plates, the liquid crystalcell thus arranged functions as a liquid crystal optical modulationdevice of which optical characteristics vary depending upon the polarityof an applied voltage. Further, when the thickness of the liquid crystalcell is sufficiently thin (e.g., 1 micron), the helical structure of theliquid crystal molecules is released without application of an electricfield whereby the dipole moment assumes either of the two states, i.e.,Pa in an upper direction 314a or Pb in a lower direction 314b, thusproviding a bistability condition, as shown in FIG. 31. When an electricfield Ea or Eb higher than a certain threshold level and different fromeach other in polarity as shown in FIG. 31 is applied to a cell havingthe above-mentioned characteristics, the dipole moment is directedeither in the upper direction 314 a or in the lower direction 314bdepending on the vector of the electric field Ea or Eb. Incorrespondence with this, the liquid crystal molecules are oriented toeither a first orientation state 313a or a second orientation state313b.

When the above-mentioned ferroelectric liquid crystal is used as anoptical modulation element, it is possible to obtain two advantages.First is that the response speed is quite fast. Second is that theorientation of the liquid crystal shows bistability. The secondadvantage will be further explained, e.g., with reference to FIG. 31.When the electric field Ea is applied to the liquid crystal molecules,they are oriented in the first stable state 313a. This state is stablyretained even if the electric field is removed. On the other hand, whenthe electric field Eb of which direction is opposite to that of theelectric field Ea is applied thereto, the liquid crystal molecules areoriented to the second orientation state 313b, whereby the directions ofmolecules are changed. Likewise, the latter state is stably retainedeven if the electric field is removed. Further, as long as the magnitudeof the electric field Ea or Eb being applied is not above a certainthreshold value, the liquid crystal molecules are placed in therespective orientation states. In order to effectively realize highreponse speed and bistability, it is preferable that the thickness ofthe cell is as thin as possible and generally 0.5 to 20 microns,particularly 1 to 5 microns.

As described above, according to the present invention, it is possibleto suppress the occurrence of flickering even in a low frame frequencydriving at a low temperature, thus providing an improved displayquality. According to another aspect of the above effect, it has becomepossible to realize a high-quality display free from flickering over awide temperature range ranging from a low temperature to a hightemperature. The present invention further realizes a gradationaldisplay with suppression of flickering caused by scanning drive at a lowfrequency.

According to the present invention, it is also possible to have a largedrive margin and provide a constant contrast. Particularly, it ispossible to prevent the occurrence of a pale black background stripepattern and provide a high-quality display free from image flow.

What is claimed is:
 1. A liquid crystal apparatus, comprising:a) aliquid crystal device comprising an electrode matrix comprising aplurality of substantially parallel scanning electrodes and dataelectrodes intersecting said scanning electrodes, and a liquid crystal;and b) drive means including first drive means for sequentially applyinga scanning selection signal to said scanning electrodes two or morescanning electrodes apart between successively selected scanningelectrodes in one vertical scanning and for effecting one picturescanning by scanning said scanning electrodes in at least two verticalscannings, wherein during a latter one of two consecutive verticalscannings of the at least two vertical scannings in one picturescanning, the scanning selection signal is applied to scanningelectrodes which are not adjacent to scanning electrodes to which thescanning signal is applied in a former one of the two consecutivevertical scannings, and second drive means for applying data signals insynchronism with the scanning selection signal.
 2. An apparatusaccording to claim 1, wherein said first drive means comprises means forapplying the scanning selection signal to said scanning electrodes 4 ormore scanning electrodes apart in one vertical scanning.
 3. An apparatusaccording to claim 1, wherein said first drive means comprises means forapplying the scanning selection signal to said scanning electrodes 5-20scanning electrodes apart in one vertical scanning.
 4. An apparatusaccording to claim 1, wherein said first drive means comprises means forapplying the scanning selection signal to said scanning electrodes Nscanning electrodes apart (N is an integer of 2, 3, 4, . . .) in onevertical scanning, and one picture scanning is effected in (N+1) timesof vertical scanning.
 5. An apparatus according to claim 1, wherein thescanning selection signal is a signal having a voltage of one polarityand a voltage of the other polarity with respect to the voltage level ofa scanning electrode to which the scanning selection signal is not beingapplied.
 6. An apparatus according to claim 1, wherein said liquidcrystal comprises a ferroelectric liquid crystal.
 7. A liquid crystalapparatus, comprising:a) a liquid crystal device comprising an electrodematrix comprising a plurality of substantially parallel scanningelectrodes and data electrodes intersecting said scanning electrodes,and a liquid crystal; and b) driving means including first drive meansfor sequentially applying a scanning selection signal to said scanningelectrodes two or more scanning electrodes apart between successivelyselected scanning electrodes in one vertical scanning and for effectingone picture scanning by scanning said scanning electrodes in at leasttwo vertical scannings, wherein during a latter one of two consecutivevertical scannings of the at least two vertical scannings in one picturescanning, the scanning selection signal is applied to scanningelectrodes which are not adjacent to scanning electrodes to which thescanning signal is applied in a former one of the two consecutivevertical scannings, the scanning selection signal comprising a formervoltage of one polarity and a latter voltage of the other polarity withrespect to the voltage level of a non-selected scanning electrode; andsecond drive means for applying to all or a prescribed part of the dataelectrodes a voltage signal providing a voltage for causing oneorientation state of the liquid crystal in combination with the formervoltage of one polarity of the scanning selection signal, and applyingto a selected data electrode among said all or a prescribed part of thedata electrodes a voltage signal providing a voltage for causing theother orientation state of the liquid crystal and to the other dataelectrodes a voltage signal providing a voltage not changing theprevious state of the liquid crystal, respectively, in combination withthe latter voltage of the other polarity.
 8. An apparatus according toclaim 7, wherein said first drive means comprises means for applying thescanning selection signal to said scanning electrodes 4 or more scanningelectrodes apart in one vertical scanning.
 9. An apparatus according toclaim 7, wherein said first drive means comprises means for applying thescanning selection signal to said scanning electrodes 5-20 scanningelectrodes apart in one vertical scanning.
 10. An apparatus according toclaim 7, wherein said first drive means comprises means for applying thescanning selection signal to said scanning electrodes N scanningelectrodes apart (N is an integer of 2, 3, 4, . . . ) in one verticalscanning, and one picture scanning is effected in (N+1) times ofvertical scanning.
 11. An apparatus according to claim 7, wherein saidliquid crystal comprises a ferroelectric liquid crystal.
 12. A liquidcrystal apparatus, comprising:a liquid crystal device comprising anelectrode matrix comprising a plurality of substantially a liquidcrystal device comprising an electrode matrix comprising a plurality ofsubstantially parallel scanning electrodes and data electrodesintersecting said scanning electrodes, and a liquid crystal; drivingmeans including a first drive means for sequentially applying a scanningselection signal to said scanning electrode two or more scanningelectrodes apart between successively selected scanning electrodes inone vertical scanning and for effecting one picture scanning by scanningsaid scanning electrodes in at least two vertical scannings, and seconddrive means for applying data signals in synchronism with the scanningselection signal, and wherein during a latter one of two consecutivevertical scannings of the at least two vertical scannings in one picturescanning, the scanning selection signal is applied to scanningelectrodes which are not adjacent to scanning electrodes to which thescanning signal is applied in a former one of the two consecutivevertical scannings, the scanning selection signal comprising a formervoltage of one polarity and a latter voltage of the other polarity withrespect to the voltage level of a non-selected scanning electrode;second drive means for applying to all or a prescribed part of the dataelectrodes a voltage signal providing a voltage for causing oneorientation state of the liquid crystal in combination with the formervoltage of one for causing the other orientation state of the liquidcrystal and to other data electrodes a voltage signal providing avoltage not changing the previous state of the liquid crystal,respectively, in combination with the latter voltage of the otherpolarity; and polarizing means having polarization axes crossing eachother which are so disposed that a dark optical state is formed when theliquid crystal is oriented to said one orientation state thereof.
 13. Anapparatus according to claim 12, wherein said liquid crystal comprises aferroelectric liquid crystal.